

package com.hazelcast.client;

import javax.annotation.Nonnull;
import java.util.Collection;
import java.util.UUID;

/**
 * ClientService allows you to query connected {@link Client}s and
 * attach/detach {@link ClientListener}s to listen to connection events.
 * <p>
 * All the methods are thread-safe.
 *
 * @see Client
 * @see ClientListener
 */
public interface ClientService {

    /**
     * Returns all connected clients to this member.
     *
     * @return all connected clients to this member
     */
    @Nonnull
    Collection<Client> getConnectedClients();

    /**
     * Adds a ClientListener.
     * <p>
     * When a ClientListener is added more than once, it will receive duplicate events.
     *
     * @param clientListener the ClientListener to add
     * @return registration ID which can be used to remove the listener using the {@link #removeClientListener(UUID)} method
     * @throws java.lang.NullPointerException if clientListener is {@code null}
     */
    @Nonnull
    UUID addClientListener(@Nonnull ClientListener clientListener);

    /**
     * Removes a ClientListener.
     * <p>
     * Can safely be called with a non existing ID, or when the ClientListener already is removed.
     *
     * @param registrationId ID of the ClientListener registration
     * @return {@code true} if registration is removed, {@code false} otherwise
     * @throws java.lang.NullPointerException if registration ID is {@code null}
     */
    boolean removeClientListener(@Nonnull UUID registrationId);
}
